optimise view count calculation query

app/models/user.rb

@@ -329,12 +329,13 @@ class User < ActiveRecord::Base
             (SELECT v.user_id,
                     COUNT(DISTINCT parent_id) AS c
              FROM views AS v
-             WHERE parent_type = 'Topic'
+             WHERE parent_type = 'Topic' AND v.user_id IN (
+                SELECT u1.id FROM users u1 where u1.last_seen_at > :seen_at
+             )
              GROUP BY v.user_id) AS X
             WHERE
                     X.user_id = users.id AND
-                    X.c <> topics_entered AND
-                    users.last_seen_at > :seen_at
+                    X.c <> topics_entered
     ", seen_at: 1.hour.ago
 
     # Update denormalzied posts_read_count
@@ -343,10 +344,12 @@ class User < ActiveRecord::Base
               (SELECT pt.user_id,
                       COUNT(*) AS c
                FROM post_timings AS pt
+               WHERE pt.user_id IN (
+                  SELECT u1.id FROM users u1 where u1.last_seen_at > :seen_at
+               )
                GROUP BY pt.user_id) AS X
                WHERE X.user_id = users.id AND
-                     X.c <> posts_read_count AND
-                     users.last_seen_at > :seen_at
+                     X.c <> posts_read_count
     ", seen_at: 1.hour.ago
   end
 

db/migrate/20131002070347_add_user_id_parent_type_index_on_views.rb

@@ -0,0 +1,5 @@
+class AddUserIdParentTypeIndexOnViews < ActiveRecord::Migration
+  def change
+    add_index :views, [:user_id,:parent_type,:parent_id]
+  end
+end